According to prior arts, it has been known to obtain SOI including a handle substrate composed of a transparent and insulating substrate and called Silicon on Quartz (SOQ), Silicon on Glass (SOG) or Silicon on Sapphire (SOS), and adhered wafer by bonding a transparent wide-gap semiconductor including GaN, ZnO, diamond, AlN or the like to a donor substrate such as silicon. SOQ, SOG, SOS and the like are expected for applications such as a projector and high frequency device due to the insulating property and transparency of the handle substrate. Further, the composite wafer, which is obtained by adhering a thin film of the wide-gap semiconductor to the handle substrate, is expected in applications such as a high performance laser and power device.
It has been used, in a high frequency switching IC or the like, an adhered substrate including a base substrate of sapphire having characteristics of high insulating property, low dielectric loss and high thermal conduction and a silicon thin film formed on the surface for providing a semiconductor device. According to prior arts, it was generally performed a method of forming a silicon region on a base substrate by epitaxial growth. It has recently developed a method of directly bonding them to contribute to the improvement of performance of the semiconductor device (Patent documents 1, 2 and 3).
However, as sapphire is expensive, it is desired to use a substrate made of a material, other than sapphire, for the handle substrate for reducing the cost. As to the development of the bonding technique described above, it has been proposed various kinds of handle substrates of materials other than sapphire, such as quartz, glass, alumina or the like.
Among them, polycrystalline transparent alumina had been used for a luminous vessel for a high-luminance discharge lamp and a dummy wafer for a semiconductor production system. By using a material of high purity and densifying it through sintering in reducing atmosphere at a high temperature, it is possible to realize excellent characteristics such as high insulation, low dielectric loss and high thermal conduction comparable to those of sapphire alleviating the need of a crystal growing step requiring a high cost (Patent documents 4, 5 and 6).
In the case that a translucent base substrate is used, it cannot be appropriately detected with an optical sensor in a semiconductor production system to result in troubles in the system. For preventing this, it was proposed methods of subjecting a back face of a base substrate to sandblasting, lithography or laser processing to roughen it (Patent documents 7, 8, 9, 10, 11 and 12). It was further proposed a method of lowering a density of a crystalline translucent substrate to reduce its translucent property (Patent document 12).